If you pull up Google maps and look at the area surrounding Tashkent, the borders are very odd between these three countries. Borders do not seem to be based on rivers or mountain ranges. Another interesting note is there are some cities owned by one country that are completely enveloped by another (see Vorkuh, Tajikistan which is completely surrounded by Kyrgyzstan, cut off from the rest of the country). How did the modern day borders of these countries in this specific region develop?
EDIT: *the in the title, not "he"
These borders were based upon the borders of the old Soviet republics (prior to its fall) These were drawn in the early years of the USSR based upon intensive ethnographic mapping by Soviet social scientists.
Essentially, they send out vast amounts of people into central Asia to collect data on language and ethnicity in each village, the borders were meticulously drawn based upon this data.
Have a read Francine Hirsch's book Empire of Nations: Ethnographic knowledge and the making of the Soviet Union